As for European specifically, maybe the commenter was talking about data protection laws. If not, maybe (in many European countries at the moment) less national or business background of ruthlessness.

I was thinking something different: I wonder whether Mozilla considered GitLab or Codeberg, which are the other two I know that are popular with open source projects that don't trust GitHub since it sold out to Microsoft.

(FWIW, Microsoft has been relatively gentle or subtle with GitHub, for whatever reason. Though presumably MS will backstab eventually. And you can debate whether that's already started, such as with pushing "AI" that launders open source software copyrights, and offering to indemnify users for violations. But I'd guess that a project would be pragmatically fine at least near term going with GitHub, though they're not setting a great example.)

I've used Codeberg for some projects and while their work and services are impressive and their progress steady and good, it's really not a proper alternative to Github for many use-cases.

"It depends", as always, but codeberg lacks features (that your use-case may not need, or may require), uptime/performance (that may be crucial or inconsequential to your use-case), familiarity (that may deter devs), integration (that may be time-consuming to build yourself or be unnessecary for your case) etc etc.